Building the eyes that look into the cosmos

Department of Astronomy—Motohara Laboratory

Kentaro Motohara
Associate Professor
Graduate School of Science
Institute of Astronomy

Professor Motohara graduated from the University of Tokyo with a BS in Astronomy in 1995, and from Kyoto University with a PhD in Astrophysics in 2000. In 2000, he was a support astronomer for the Subaru Telescope. He became an Assistant Professor at the Institute of Astronomy in 2001, and started at his current position in 2010.

One approach to studying the origin of the cosmos is the observation of celestial objects that were created immediately after the universe was born. The light emanating from such objects allows us to peer back into the past.

However, in an expanding universe, objects in the distant past are very far from Earth, and the farther away they are the faster they are receding from us. This is a result of Hubble’s law, which states that the speed at which two points move away from each other is positively proportional to the distance between them. Therefore, the light from objects that are extremely far away and rapidly receding from Earth is strongly red-shifted due to the Doppler effect, and infrared observations at wavelengths longer than those of visible light become important.

Professor Kentaro Motohara studies distant galaxies by examining infrared light to learn about their formation and evolution. Infrared light shows us things that cannot be seen by visible light. According to Motohara, there are two primary uses for infrared cameras: “One is observation of distant objects. The other is observing objects that are obscured by dust or gas, because these materials are transparent to infrared light.”

Places with dense dust and gas are also active areas for star formation. A better understanding of the process by which stars are formed is expected to provide clues to the origins of stars and galaxies.

Still, infrared observations come with challenges not encountered in visible light observations. “Astronomical observations are performed using a telescope to gather light (visible or infrared), and a camera to turn that light into images,” Motohara says. “Visible light can be collected by cameras at room temperature, but to obtain sufficient sensitivity using infrared sensors, they should be cooled to less than –200 °C. That makes the instrument much larger and harder to develop.”

One feature of the Motohara Laboratory is that it works both on observation and on the development of new instruments. This is attractive to students, and as Ken Tateuchi (D2) puts it, “It’s lots of fun to build an instrument, use it to carry out observations, and produce science based on what you get.”

Their current project is the SWIMS infrared camera (upper right photo), intended for use in large telescopes. This will be the main camera for the 6.5 m telescope at the University of Tokyo Atacama Observatory (TAO) in the Atacama Desert in the mountains of Chile, scheduled to begin operating in 2017. In preparation, they are now verifying the camera’s performance by mounting it onto a simulator of the telescope (the pale blue stand at the bottom of the photo) and looking for ways to improve it.

The TAO is located at an altitude of 5640 m above sea level, which is the highest astronomical observatory on Earth. That location was selected for a reason—water vapor in the atmosphere absorbs infrared radiation, an effect that is reduced at higher altitudes. Another deciding factor is that it is a desert region. A small, 1-m telescope called miniTAO began operation there in 2009. It has an infrared camera called ANIR developed at the Motohara Laboratory, and it successfully captured images of hydrogen gas obscured by dust in the Galactic Center.

Lab members travel to the location twice a year, where they spend a total of two months living and working together. This is necessary to install cameras and perform observations. “It’s cold there, and the air is uncomfortably thin,” says Soya Todo (M1). “It’s inconvenient and hard, but it teaches me perseverance,” he says with a laugh. Yutaro Kitagawa (M2) says, “Living together brings us closer, and that’s a huge help when developing hardware, which requires a lot of teamwork.”

Developing a new instrument takes years and is fraught with problems. Once that is complete, the next task is performing arduous observations in the wilderness. What sustains them through all their efforts is the thrill of being the first humans to see new things.

“It’s hard work, but there’s nothing like the joy of seeing images taken by a camera we built,” Motohara says.

This is how we create new eyes that allow us to see the cosmos.

The SWIMS infrared camera, scheduled for installation on the TAO 6.5-m telescope. This is tested by installing it on the light blue simulator in the photo at the bottom of this page.The Galactic Center behind the miniTAO dome.

Student Evaluations
“He takes our ideas very seriously.” (Ken Tateuchi, D2)
“He’s created an atmosphere where it’s very easy to come to him with questions.” (Yutaro Kitagawa, M2)
“I’ve never met anyone so smart.” (Soya Todo, M1)

― Office of Communication ―